I spent about 9 months going there on an almost weekly basis for work last year/early this year.
Stuttgart is a nice place, I found the people to be really friendly, the beer good, and the city nice. It is hot in the summer and cold in the winter, and not too far away from the foothills of the alps for weekend trips. It isn't a big city, and is surrounded by hills, which makes it feel more like a big town than a city. The public transport system is excellent too, and I have never felt threatened using it late at night.
You can get by without knowing much/any German, my experience of working in the car industry in Stuttgart is you can ask questions in English, and get answers in English! 🙂